EDA – Week 5

Comparing Batches

I recently finished grading your “comparing batches” homework and here are some remarks on some common issues where you lost points.

Issue 1:  What is the Point of the Assignment?

We want to compare batches in a simple way.  A simple comparison is say something like “Batch 2 tends to be 10 smaller than Batch 1”.  We can make a simple comparison when the batches have similar spreads.  In both of your problems, this wasn’t the case.  The reason why we did all of the work (construct a spread vs level plot, etc) was to find a reexpression so that the is not a dependence between spread and level and the batches have similar spreads on the new reexpressed scale.  If you have found a reasonable reexpression, then please compare the batches on the new scale.  It is not okay to say that one batch is larger than another batch — we’d like to know how much larger.  Many of you didn’t do this on your homework.

Issue 2:  Did My Reexpression Work?

The reason why we reexpress is to remove the dependence between spread and level.  How can one check if the reexpression works?  Well, just construct a new spread-level plot on the reexpressed data and comment if there remains a dependence between spread and level.  If there is some dependence, suggest the choice of a new reexpression that may help.

Issue 3:  Be Nice to Your Grader

I am grading your homework and I really appreciate if you give me what I am calling “tidy work”.  Here are some characteristics of tidy work:

• Just display the relevant R work.  Don’t show me anything that is not relevant to what is being asked.
• Always explain what each graph is showing us.  I don’t like naked graphs that have no accompanying explanation.
• Explain, explain, explain — I will never take points off if you write too much.

Last, please contact me if you don’t understand the question or if you have any R issues.  It is not acceptable to simply say “this function didn’t work” on your homework.  Generally, I try to be quick in responding to student requests.

Your Assignment this Week

Wait … it appears that you don’t have any work due this week.  Enjoy the cooler weather and we will be looking at reexpressions more thoroughly next week.

EDA Trivia Question — send answer to albert@bgsu.edu

One of John Tukey’s collaborators was a famous British statistician who taught at Yale.  (Hint — this statistician is famous for his “quartet”.) . This collaborator wrote a book on statistical computation using a particular programming language.  What was the name of the statistician and name of that programming language?